ASC-665 Use sys-test dev branch for experiment job
ASC-665 Use sys-test dev branch for experiment job

This commit sets the value of `SYS_TEST_BRANCH` to `dev` if the CI job
it is running on is the experimental-asc job. This job is specifically
for running system tests under development. It is designed to test
against the `master` branch of `rpc-openstack`, but should not run the
`master` branch of `rpc-openstack-system-tests` because that branch is
used for production CI jobs.

BjoernT/rpc-openstack,jacobwagner/rpc-openstack,rcbops/rpc-openstack,jacobwagner/rpc-openstack,rcbops/rpc-openstack,BjoernT/rpc-openstack